Pinboard with ladder type contact springs



I 061531, 1967 MCFADDEN 3,350,676

PINBOARD WITH LADDER TYPE CONTACT SPRINGS 2 Sheets-Sheet 1 Filed May 6,1965 INVENTOR.

BRucE RKHAMS M FAbpeN BY M, m r W Oct. 31, 1967 R. MCFADDEN 3,350,676

PINBOARD WITH LADDER TYPE CONTACT SPRINGS Filed May 6, 1965 2Sheets-Sheet 2 INVENTOR.

I LBRucE RK ARv MLFADDEN United States Patent 3,350,676 PINBOARD WITHLADDER TYPE CONTACT SPRINGS Bruce Richard McFadden, Harrisburg, Pa.,assignor to AMP Incorporated, Harrisburg, Pa. Filed May 6, 1965, Ser.No. 453,722 9 Claims. (Cl. 339-18) ABSTRACT OF THE DISCLOSURE A pinboardis disclosed for interconnecting electrical circuit paths by theinsertion of a conductive pin selectively in a matrix of conductivespring members. The conductive spring members are of a ladder-likeconfiguration wherein the rungs of the ladder define tie points forspring systems defined by the sides of the ladder. An insulating blockis provided having apertures therein to receive conductive pins andgrooves aligned with the apertures to house the conductive springmembers. The spring members are made to be of a width less than thewidth of the grooves but greater than half of the groove width in orderto eliminate tolerances and to assure the proper insertion of conductivepin members between the sidewalls formed by the ladder-like constructionof the conductive spring members.

Background of the invention The pinboard represents a type multiplecoordinate switch wherein selected interconnections are accomplishedthrough the insertion of a conductive pin member between isolatedcontacts bussed to input and output leads. The usual constructionincludes a laminated insulating block structure designed to holdconductive strips carrying contact springs in isolated and intersectingrelationship registered with apertures in the insulating blockstructure. The problem with most of the prior art devices is one ofcomplexity which results in high manufacturing cost and poorreliability. Complexity arises by virtue of the need to maintain a largenumber of insulating and conductive components in rather exactalignment. For example, in a typical pinboard capable of permitting aselected interconnection of any one of ten input leads to any one of tenoutput leads it is necessary to provide 100 connection paths. In anaccepted prior art pinboard construction this is accomplished through anassembly including four or more insulating boards containing some twentyconductive strips each having at least eleven separate contact springs(a total of 220) fixed within the boards such that the contact areas ofthe springs are in exact alignment with apertures for pin insertion inthe board members. This means that considerable care must be exercisedin the production of the various insulating and conductive componentswith respect to length, width and center-to-center spacing andconsiderable care must be exercised in assembly of these components toachieve the necessary registry of the parts. Close tolerances inmanufacture and assembly means high relative cost and can mean pooroverall reliability which is related to the performance of eachcomponent.

Summary of the invention This invention relates to a pinboard assemblyof the type utilized to selectively interconnect electrical circuits.

Accordingly, it is one object of the present invention to provide apinboard assembly which is inexpensive and yet reliable. It is anotherobject of the invention to provide a pinboard construction utilizing anovel contact spring which substantially reduces the need to maintainclose tolerances with respect to manufacture and assembly of pinboarddevices. It is a further object of the invention to provide a newcontact spring system for pinboards and like devices.

The present invention overcomes the foregoing problems and attains itsobjectives through an insulating board construction employing twoidentical board members which inter-digitate to captivate spring contactstrips contained therein. The spring contact members are of a ladderlike configuration wherein the rungs of the ladder define tie points forthe spring systems defined by the size of the ladder. The contact springmembers include further details to prevent scouring of the pins insertedtherein and to further relieve tolerances of manufacture and assembly.

In the drawings:

FIGURE 1 is a perspective of a pinboard in accordance with the presentinvention having a corner thereof sec tioned to show interiorconstruction;

FIGURE 2 is a perspective showing two of the contact members of theinvention positioned as in use in the board of FIGURE 1 and having a dieconductive pin inserted therebetween;

FIGURE 3 is a plan view, somewhat enlarged from actual size, showingportions of the contact member of the invention positioned within aninsulating board member;

FIGURE 4 is a section taken through lines 44 of FIGURE 3;

FIGURE 5 is a section taken through lines 5-5 of FIGURE 3; and

FIGURE 6 is a sectional view of an alternative construction for thespring member of the invention.

Description of the preferred embodiment 09 the invention Referring nowto FIGURE 1, the pinboard assembly is shown as 10 to include a pair ofinsulating board members 12 and 14; at least the upper member containingan array of apertures 16. The board members are, for the purposes ofillustration, fastened at each corner by rivets, screws or the like,shown as 18. Input leads are applied to the assembly 10 from the rear ofthe board or in some other suitable fashion and selected connections areaccomplished by the insertion of pins such as 20; one being showninserted in the board and one being shown positioned above the board forinsertion.

The boards 12 and 14 are identical and may preferably be from the samemold, if molded. Each of the boards includes a series of parallelgrooves 12a separated by a series of parallel projections shown as 12bwhich carry further and integral projections 120. As assembled thegroove projection faces of the board are disposed in face to facerelationship and oriented at right angles so that the various groovesand projections of one board intersect the grooves and projections ofthe other board. Within each groove of the upper and lower board membersis a contact spring like the springs 26 and 28 shown in FIGURE 2 whichheld against lateral displacement by the projections 12b between groovesand held against transverse displacement by the further projectionswhich extend from one board over into the other board to hold the springmembers of that board in position.

As a preferred way of accomplishing the input and output connections thegeneral board construction reference is made to copending US.application Ser. No. 441,700 filed Mar. 22, 1965 in the name of WinfieldLoose.

With the boards 12 and 14 properly oriented and assembled as indicatedin FIGURE 1 insertion of a pin member 20 within an aperture 16 willresult in an interconnection between one of the upper contact memberssuch as 26 and one of the lower contact members such as 28; theconnection being made through the conductive body of the pin member. Thepins 20 may be considered as solid 3 members comprised of a conductivebarrel 24 and an insulating handle 22 although it is contemplated thatdiode pins or live pins of the type described in the aforementionedLoose application may also be employed.

Each contact member is of the general configuration shown in FIGURE 2with respect to contact member 26. The member includes sides ofconductive metallic strip stock shown as 26a and 26b in open parallelrelationship joined at the bottom by members 260. This structure forms aladder arrangement wherein 26a and 261) are the sides and members 260may be thought of as rungs. The sides 26a and 26b should have springcharacteristics and various grades of brass or beryllium copper havebeen found suitable for this purpose. The contact members 26 arepreferably formed in the flat from sheet stock material by stamping andblanking and then formed into the configuration shown and plated atleast on the interior surfaces with an alloy adapted to provide a lowresistance path and to prevent corrosion. In a typical construction boththe pin barrel 24 and the members 26 and 28 would be furnished with astandard gold over nickel plating.

Referring now to FIGURE 3, a contact member 26 is shown positioned in agroove 12a. As part of the invention the width W of the contact memberrelative to the width W of the groove is made such that there isconsiderable play between the member and the walls of the groove. Thismeans that there is practically no criticality of tolerance as to thewidth of the spring member or as to the width of the groove. It ispreferred to make W greater than /2 W so that no combination oftolerances or position of the contact member within the groove canresult in the pin body 24 passing outside of the contact member sidesrather than therebetween. In an actual unit made of stock 0.010 inchwherein W was equal to 0.178 inch, the interior width of the contactmember 26 was made 0.080 inch (making W equal to 0.090 inch) and theaperture 16 was made to be 0.102 inch in diameter. The spacing betweenrungs 26c may be as shown as in FIGURE 3 by S to be approximately equalto the center-to-center spacing of the apertures 16 and the width of thebody of the rungs should be sufiicient to adequately tie the sides 26aand 26b together and to form a point of contact for the projections 12cof the opposite board member which holds the contact members in positionin the embodiment of FIGURE 3. These projections are shown incrosssection in FIGURE 3 by dotted lines to fit between the contactmember sides and to overlap the rungs to eliminate tolerances in matingtherewith. The thickness and material characteristics of the sides 26aand 26b in conjunction with dimension S establishes the resiliency ofthe spring system of the contact members and the axial force ofinsertion of the pin necessary to spread the sides. In an actual unit Swas 0.450 inch and the sides were of 0.010 inch Phosphor bronze No. 4stock which was 0.040 inch in width. In this regard it is considered tobe important to have a spring force sufficient to define a lowresistance path between the contact strips and the pin body butinsufficient to cause inelastic stressing of the sides of the member orscouring of the contact surfaces. As will be apparent from FIGURE 3, thesides have an unstressed configuration as shown to the left relative tothe aperture 16 having no pin inserted therein and a stressed conditionshown to the right developed by the insertion of the body of 24c of thepin.

If desired, rungs may alternately be provided between each aperture withan appropriate adjustment in the thickness and hardness of the contactmember stock to provide proper resiliency.

FIGURE 4 is an enlarged cross-section showing the preferredconfiguration of the sides of the contact member to be of two upstandingand substantailly parallel beams which may be deflected as indicated bythe dotted line in a sense transverse to the longitudinal axis of themember. The upper and lower edges of each beam are preferably coined todefine a radius shown as 26d and 262. This may be readily accomplishedin the blanking operation by having the cutting die directed in movementor stroke to shear the metal downwardly on both edges of each side suchthat when the members formed into the position of FIGURE 4 the radii areleft on the interior of the member. Through the provision of theradiused edges the insertion of the pin is faciliated, the surfacestending to guide the pin and prevent damage to the contact surfaces. Inan actual unit the radius was made approximately equal to 0.012 inch.

FIGURE 5 shows a section through the rung of the contact member 26 andin the embodiment of FIGURE 3 the rung will be seen to substantiallyintersect the side members and to lay flat along the bottom of thegroove 12a. FIGURE 6 shows an alternative embodiment which with respectto the groove 12a and the aperture 16 is identical to the embodiment ofFIGURE 4. The side members of the contact members shown as 26' are alsosimilar to the embodiment shown in FIGURE 4 but the rung includes a tabindicated by 27 displaced upwardly from the floor of 12a and there areprojections 26d provided to aid in centering the member. The projection12c employed to hold the contact member 26 in position is made of alength to engage the projection and hold the contact members resilientlyin a downward sense. This serves to provide an additional relief againsttolerances since the projections may vary from a point of lightengagement with the tabs 27' to a length approximately equal to thedisplacement of a tab to a flat position along the floor of the groove.

Having thus described my invention I now define it in the appendedclaims.

What is claimed is:

1. In an assembly for selectively interconnecting electrical circuits,an insulating block structure having rows of transverse aperturestherein, a series of conductive pin members adapted to be inserted insaid apertures, a plurality of grooves within said block structuregenerally aligned with the rows of apertures and of a given width, aconductive contact member in each groove including a pair of fiat stripside members of spring material extending along the groove length, saidside members having in terior facing contact surfaces in substantiallyparallel relationship normal to the axis to the said apertures so as toreceive a pin member inserted therebetween, means joined to said sidemembers at spaced points along the length thereof for holding saidmembers and said surfaces spaced apart by a distance less than saidgiven width but greater than one-half said given width and less than thesaid apertures to provide resiliency to said side members by providingspring beams between said points and assure pin member insertion betweensaid surfaces.

2. The assembly of claim 1 wherein said means is comprised of a seriesof rungs disposed at right angles to said side members, said rungs beingpositioned in said grooves between said apertures.

3. The assembly of claim 1 wherein said means is comprised of rungsdisposed along the length of the contact member between the saidapertures, said rungs being integral with the material of each sidemember.

4. The assembly of claim 1 wherein said side members are radiused at thetop and bottom edges to prevent scouring of a pin member duringinsertion and withdrawal in said assembly.

5. The assembly of claim 1 wherein said block structure is comprised ofa pair of insulating boards each having rows of transverse aperturestherein and each having said plurality of grooves therewithin, the saidboards being arranged with the grooves thereof at right angles, eachboard including bordering the grooves thereof a projection extendinginto the groove of the opposite board to hold the contact member thereinagainst transverse movement relative to said assembly.

6. The assembly of claim wherein said means includes a projectionadapted to engage the projection of said boards.

7. In a pinboard assembly of the type utilized to selectivelyinterconnect electrical circuits, a pair of boards of insulatingmaterial each including a plurality of rows of apertures transverse tothe major surface of the board, a plurality of parallel grooves of agiven width generally aligned with the board apertures, and a pluralityof first projections between said grooves and continuous therewith, eachboard further including a plurality of second projections extending fromsaid first projections and noncontinuous along the length of said firstprojections, a contact member in each groove comprised of a pair ofsidewalls each defined by a fiat strip of conductive material and havingthe interior surfaces thereof in spaced and substantially parallelrelationship extending continuously along said grooves, the saidsidewalls being held by rung portions at points spaced along the lengththereof to define spring beams between said rungs formed of the materialof said sidewalls, the said sidewalls being spaced apart by .a distanceless than the said given width of said grooves and less than thediameter of said apertures whereby the insertion of a conductive pinmember in said apertures will engage the interior surfaces of saidsidewalls under a spring force developed in said sidewall, the saidsecond projections extending between said sidewalls to engage the saidrungs between said apertures and hold said contact members in positionin said pinboard.

8. In a pinboard assembly of the type adapted to be utilized toselectively interconnect electrical circuits comprising an insulatingblock structure having rows of apertures extending transverselytherethrough adapted to receive conductive pin members, a plurality ofgrooves within said block structure, each groove being aligned with arow of apertures and of a width greater than the diameter of saidapertures, a contact member disposed in each groove formed of flat stripconductive material having spring characteristics, the said contactmember including parallel sides extending along said grooves, said sidesbeing held by rungs disposed at points along the lengths of said contactmember and spaced apart by a distance less than the diameter of saidapertures but greater than onehalf the width of said grooves so that atleast one side wall of said contact member is always secant to a saidaperture.

9. The assembly of claim 8 wherein projections are included extendingout from said sides to engage the walls of said grooves and center saidcontact members in said grooves.

References Cited UNITED STATES PATENTS 2,251,403 8/1941 Frank et al33922 2,922,135 1/1960 Hoberg et a1. 339-18 3,027,534 3/1962 Deakin33918 3,170,745 2/1965 Deakin 33918 3,245,024 4/ 1966' Evans 33917FOREIGN PATENTS 893,066 10/1953 Germany. 896,105 5/1962 Great Britain.

MARVIN A. CHAMPION, Primary Examiner. PATRICK A. CLIFFORD, AssistantExaminer.

1. IN A ASSEMBLY FOR SELECTIVELY INTERCONNECTING ELECTRICAL CIRCUITS, ANINSULATING BLOCK STRUCTURE HAVING ROWS OF TRANSVERSE APERTURES THEREIN,A SERIES OF CONDUCTIVE PIN MEMBERS ADAPTED TO BE INSERTED IN SAIDAPERTURES, A PLURALITY OF GROOVES, WITHIN SAID BLOCK STRUCTURE GENERALLYALIGNED WITH THE ROWS OF APERTURES AND OF A GIVEN WIDTH, A CONDUCTIVECONTACT MEMBER IN EACH GROOVE INCLUDING A PAIR OF FLAT STRIP SIDEMEMBERS OF SPRING MATERIAL EXTENDING ALONG THE GROOVE LENGTH, SAID SIDEMEMBERS HAVING INTERIOR FACING CONTACT SURFACES IN SUBSTANTIALLYPARALLEL RELATIONSHIP NORMAL TO THE AXIS TO THE SAID APERTURES SO AS